and Necrotic Cells Quantitations and Evidence for Their Origin from Apoptotic DNA Fragments in the Blood Plasma of Cancer Patients

ABSTRACT Increased levels of DNA fragments have frequently been found in theblood plasma of cancer patients. Published data suggest that only afraction of the DNA in blood plasma is derived from cancer cells. How-ever, it is not known how much of the circulating DNA is from cancer orfrom noncancer cells. By quantitative methylation-specific PCR of thepromoter region of the CDKN2A tumor suppressor gene, we were able toquantify the fraction of plasma DNA derived from tumor cells. In theplasma samples of 30 unselected cancer patients, we detected quantities oftumor DNA from only 3% to as much as 93% of total circulating DNA.We investigated possible origins of nontumor DNA in the plasma anddemonstrate here a contribution of T-cell DNA in a few cases only. Toinvestigate the possibility that plasma DNA originates from apoptotic ornecrotic cells, we performed studies with apoptotic (staurosporine) andnecrotic (staurosporine plus oligomycin) cells in vitro and with mice afterinduction of apoptotic (anti-CD95) or necrotic (acetaminophen) liver in-jury. Increasing amounts of DNA were found to be released in thesupernatants of cells and in the blood plasma samples of treated animals.A clear discrimination of apoptotic and necrotic plasma DNA was possibleby gel electrophoresis. The same characteristic patterns of DNA fragmentscould be identified in plasma derived from different cancer patients. Thedata are consistent with the possibility that apoptotic and necrotic cells area major source for plasma DNA in cancer patients.